Finding venues and effective strategies to engage young men who are at high risk of transmitting and acquiring HIV has remained a persistent challenge in the field of HIV prevention. The proposed study applies innovative, multilevel intervention methods to engage social networks of young men in Dar es Saalam, Tanzania to reduce HIV risk and the perpetration of gender-based violence. Prior work by our team in this setting identified networks of young men at high risk for HIV who belong to what are called camps. Camps are semiformal organizations of youth, mostly men, who socialize regularly in a fixed location. Through funding from NIMH (R21MH80577) we enumerated and described 73 camps within one ward (equivalent to US census tract) of Dar es Salaam. Based on findings from the preliminary studies, we developed and piloted an intervention that combines microfinance with health promotion training for camp leaders. The intervention addressed the structural and social determinants of men's risk for HIV, while also leveraging the strong network ties that exist among men in camps. Building on this preliminary work the proposed study has two aims: 1) To enumerate and characterize camps in four wards of Dar es Salaam where young men at high risk for HIV acquisition and transmission socialize in order to generate a pool of camps for inclusion in the larger trial; 2) To conduct a cluster randomized trial among 2808 men belonging to 54 camps located within four wards of Dar es Salaam, to determine whether men in camps randomized to receive a microfinance and health leadership intervention have a lower incidence of sexually transmitted infections and report perpetrating less physical or sexual violence against female sexual partners as compared to men belonging to camps that are randomized to a control condition. Secondary outcomes include HIV risk and protective behaviors including: uptake of HIV counseling and testing; a reduction in unprotected sexual intercourse; correct and consistent condom use; deferral of sexual debut; a reduction in the number of sexual partners and sexual concurrency. Key mediators are hope, future orientation, collective efficacy, social support and social influence. All men in the selected camps will be enrolled and followed for 30 months. Quantitative and qualitative assessments will occur at baseline, 12 months and 30 months. If the proposed multilevel intervention proves efficacious at reducing risk behaviors among young men, the approach is one that can be adapted, scaled-up and applied to work with young men in other global settings.